tmkhoop
Member
Posts: 25
Loc: Flint, MI
Reg: 12-13-01
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 01-20-02 03:34 AM - Post#5189
What is everyone using to test there batteries with? What kind of load are you puting on them when testing?
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Phil Cole
Member
Posts: 78
Loc: Redwood City CA USA
Reg: 02-05-01
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01-20-02 05:06 AM - Post#5190
In response to tmkhoop
I use a standard hobby-type ESV. The ESV is cheap, and can withstand bouncing about in the bottom of my flight box. It's load is a 27 Ohm resistor.Its calibration may not be that accurate, but I used it to plot a discharge curve, noting the indication every five minutes. From the plot it's obvious when the NiCd battery is discharged. Then go back 15 or 20 min. (or however long you fly for) and that's the voltage you need to see to start a flight. I generally leave an extra 10 min. safety margin and 0.1 V or so for voltages due to ambient temperature. Note that you need to know what your models discharge rate is compared to the ESV. The ESV is about 300 mA. A model heli will typically be between 500 mA and 3 A average current when it's flying.
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Jared
Senior Member
Posts: 167
Loc: Memphis
Reg: 11-02-01
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01-21-02 03:03 PM - Post#5191
In response to Phil Cole
I'm using the Gem 2000. Learn more at electrotekRC.com. Fine folks, they are.
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squirrel
Senior Member
Posts: 327
Loc: South Whitley, In ,USA
Reg: 03-17-01
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01-21-02 03:48 PM - Post#5192
In response to Jared
No load, just use a high quality meter like Fluke, Tektronix or Hewellet Packard and measure the voltage immediately after landing. If you wait to check the voltage. the cells' chemistry will generate a small increase in potential which is a false indication of the actual charge.Fred
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DavidH
Senior Member
Posts: 1555
Loc: Birmingham,AL .
Reg: 05-31-01
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01-21-02 03:52 PM - Post#5193
In response to squirrel
I use a Fluke meter with a resistor inline that puts an 800 mah load on the battery. Need to check battery under some load to get an accurate readingDavid
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Dyehard
Senior Member
Posts: 272
Loc: Richlands, Va.
Reg: 01-27-01
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01-21-02 04:16 PM - Post#5194
In response to DavidH
I just use the digital meter built into my 9Z using the 500 mil load. I checked it against my Fluke 87 and found that when the transmitter was showing 4.8 volts that it was really 5.1 volts. That leaves quite a comfortable margin. I agree that it is best to check loaded voltage right after landing. To check it unloaded will still give a much higher reading than the system will see in flight.[This message has been edited by Dyehard (edited 01-21-2002).]
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polstery
New Member
Posts: 20
Loc: Bristol,CT,USA
Reg: 01-20-02
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01-22-02 01:15 AM - Post#5195
In response to Dyehard
Tower sells some,as long as you get one with at least a 500ma load you'll be fine
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Phil Cole
Member
Posts: 78
Loc: Redwood City CA USA
Reg: 02-05-01
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01-22-02 08:48 PM - Post#5197
In response to Ergo60
Ergo,I'm aware of all that you say. However as long as you load the cells enough to make the cells deliver some current, the voltage reading is a reasonable indication of charge level. The difference between my readings and yours will simply reflect the cell and wiring resistance. If you actually see the reading drop over fifteen seconds, then the battery is pretty much discharged. The no-fly reading is one flight-time before this. I ran the discharge curves and know what voltage this is according to my ESV. My Raptor can remove about 780 mAh in 45 minutes of flying - this makes the average current about 1 A. I measured this by seeing how much further I have to go to completely discharge the battery (usually about 600 mAh), then subtract from its measured capacity (1380 mAh).
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Ergo60
Senior Member
Posts: 186
Loc: South Haven,MI USA
Reg: 09-19-01
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01-23-02 05:47 AM - Post#5196
In response to polstery
Phil, if the load resistor in your ESV is the 27 ohms as stated, then the actual load for an average of 4.8 volts would only be 177ma. My battery tester uses a 9 ohm resistor that gives me an average load current of around 533ma. This is more inline with what the heli actually draws on average. Also, you should always remember to leave the load on for at least 15 seconds and watch the reading to see if it drops. If I see to much of a drop then I know that the battery pack needs a re-charge. I also plot the discharge curves for my pack at least once a month and save the data to monitor for trends in the discharge time. I built a charger/cycler that plots this data through a serial port into excell. I first charges, and tops off the pack and then discharges it while constantly monitoring the current and voltage. We all place a really large burden on our batteries, and they are the most important part, so treat them well, and replace them when needed, they are the cheapest preventative part we have. Also remember when you buy new ones to recycle the old ones.
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